An inflatable restraint system having an air bag door that is integrally formed into an automotive vehicle instrument panel must include some provision for guiding or otherwise facilitating the opening and partial separation of that air bag door from the instrument panel that the door is integrally formed with. The air bag door in such a system opens to provide a path for an air bag to deploy through. It is desirable that whatever such provision is made includes some means for insuring that the air bag door breaks and/or tears open in a generally predictable way. This is true for driver-side inflatable restraint systems (DSIRs), passenger-side inflatable restraint systems (PSIRs) and inflatable restraint systems in vehicle door panels, quarter panels or other sidewall structures. It is also desirable for such systems to include means for insuring that portions of the door do not separate from the system when the air bag deploys and forces the door open.
The need to control breakage and/or tearing is particularly important with air bag doors that are integrally formed into hard first-surface instrument panels. The "first-surface" of a panel is the cosmetic exterior surface that would be visible to a vehicle occupant. Hard first-surface panels are typically formed by injection molding one or more plastic materials.
To close air bag deployment openings in hard first-surface instrument panels, many current PSIR systems use a separate "add-on" air bag door. One reason that current PSIR systems add on a separate air bag door in such applications is because it is difficult to cause a tear seam in an integrally formed door to break and/or tear in a predictable way under the sudden shock of a deploying air bag. Even when weakened, a tear seam that integrally joins an air bag door and a surrounding instrument panel can fracture in a ragged unpredictable manner that can affect air bag deployment.
One example of a hard first-surface system is disclosed in U.S. Pat. No. 5,472,228 assigned to Morton International and issued Dec. 5, 1995. This patent discloses a reinforced hard door with a reaction plate. When the air bag deploys, the reaction plate forces the door in a direction that will break weakened fasteners securing the door to an instrument panel.
Another of Morton's hard door concepts is shown in U.S. Pat. No. 5,533,746, issued Jul. 9, 1996. This system includes a reaction plate with reinforced lands. When the air bag deploys, it acts upon the reaction plate to cause hold down attachment rods to release from clips.
To control tearing and/or breaking, air bag doors that are integrally formed with automotive trim or instrument panels will sometimes include frangible marginal edges which are regions of weakened materials, reduced thickness or scoring and are commonly referred to as "tear seams." Tear seams are weak areas designed to tear and/or break when an air bag inflates and forces the door to open. Some of these systems also employ tethers and/or hinges that retain the air bag door to the instrument or trim panel after the door has torn and/or broken open. For example, U.S. Pat. No. 5,569,959, issued to Cooper et al., discloses an inflatable restraint assembly comprising an air bag door retainer portion integrally formed in an automotive instrument panel retainer and defined by a door perimeter. A frangible marginal edge or tear guide is included in a skin cover disposed over a foam layer that extends across the door opening. A metal hinge panel is embedded within the instrument panel retainer and spans a portion of the door perimeter. Cooper et al. also disclose a method for making such an inflatable restraint assembly. The method includes pre-molding the hinge panel into the hard instrument panel retainer portion such that the hinge panel spans the door perimeter.
With many current systems, the tear seams and/or hinges are formed in a hard instrument panel retainer portion rather than a skin cover. This can be done by a secondary operation such as casting weakened material, or cutting, grinding or laser scoring performed after a manufacturing step of integrally molding the instrument panel and door. Current systems also include tear seams formed in back surfaces opposite the outer class-A surfaces of integral instrument panel/air bag door structures to improve the aesthetic appearance of the instrument panel by concealing the presence of the door.
At least one automotive instrument panel, as shown and described in U.S. Pat. No. 5,162,092, issued to Klobucar et al., discloses an instrument panel having a tubular channel and a method for forming the channel in the panel. The tubular channel is integrally formed in the panel by injecting gas into molten panel material in a mold. The tubular channel in the Klobucar et al. instrument panel adds structural rigidity. However, Klobucar et al. does not disclose an air bag door or any other supplemental inflatable restraint component.
What is needed is an apparatus that, in response to air bag deployment, more cleanly and predictably separates and opens an air bag door that is integrally formed into an instrument panel. What is also needed is such an apparatus that helps separate and open an air bag door that is integrally formed into a hard first-surface instrument panel.